An eco-friendly way to valorize winery wastewater and sewage sludge: anaerobic co-digestion

Abstract

Anaerobic digestion (AD) of sewage sludge (SS) and anaerobic co-digestion (AcoD) of SS and wine distillery wastewater (WDW) was investigated at different hydraulic retention times (HRTs), ranging from 20 to 8 d. The mixture of SS and WDW resulted in a highly improved quality of feedstock: soluble organic matter and organic matter easily accessible for acidification increased substantially (> 60 %), while non-solubilized organic matter decreased (> 160 %). AcoD of SS:WDW consequently yields higher values of average organic matter removals (48-66 %) compared to AD of SS alone (42-58 %), in keeping with the increase in specific methane productivity (SMP) (around 45 %). Increasing the organic loading rate (OLR) or decreasing the HRT resulted in an increase in methane production (MP) and a decrease in SMP. Maximum values of MP in AD and AcoD were respectively 0.9 ± 0.2 L CH4 d-1 at an OLR of 8.2 and 5.4 kg TCOD m-3 d, corresponding to an HRT of 8 d. SMP values in AD and AcoD fell within the 200-300 L CH4 kg VS-1 and 300-400 L CH4 kg VS-1 range, respectively. This paper presents a low-cost strategy for wine producing countries to increase energy generation at wastewater treatment plants, as well as providing them with an interesting source of income